This invention relates to an insulated gate type field effect semiconductor device, especially an insulated gate field-effect transistor (abbreviated to IGFET hereinbelow) for high power, a circuit employing the devices, and a method for manufacturing the device.
IGFET's generally termed MOS (metal Oxide Semiconductor) FET's have heretofore been mainly used in LSI's for desk-top calculators etc. as switching elements of low voltages of below 10-20 V and low currents of below several mA.
As the result of research by the inventors to be described later, however, it has been revealed that IGFET's are desirably applied, not only to such uses of low voltages and low currents as has been the case up to now, but also to uses of high voltages and high currents.
The drain current of the IGFET has a negative temperature coefficient in a range of comparatively large values thereof, and does not have a positive temperature coefficient as in the collector current of a bipolar transistor. Therefore, even when a potential difference is generated on a semiconductor pellet of large area by a current flowing to an electrode, the current crowding phenomenon does not occur. Accordingly, there is little tendency for destruction due to thermal runaway to occur. The IGFET has a high input impedance, and moreover, the drain current is proportional to the square of the gate--source voltage and scarcely includes components of higher orders. It has accordingly been revealed that, when compared with the bipolar transistor, the IGFET attains a higher power gain and exhibits a characteristic of lower distortion factor.
In the IGFET, the drain current--versus--drain voltage characteristic exhibits a saturation characteristic or the so-called pentode characteristic. Therefore, the IGFET presents a better characteristic against the fluctuation of the supply voltage than a vertical type field effect transistor in which the drain current exhibits a non-saturation characteristic. In the IGFET, the values and range of the gate--source cutoff voltage can be selected far more freely than in a junction type field effect transistor. It has been revealed that a fluctuation in the gate--source capacitance and a fluctuation in the gate--drain capacitance ascribable to fluctuations in the gate voltage, the drain voltage, etc. are less in the IGFET than in the junction type field effect transistor.